1. Field of the Invention
The present invention relates to a data reproduction device and method using viterbi decoding, and more particularly, to a data reproduction device and method that can achieve a reference level optimizing the characteristic of a channel and can be applied to the reproduction of data on an optical disk.
2. Description of the Related Art
In an optical disk, a binary signal is recorded on the surface of the disk and by reading a reflected waveform when a laser beam is applied to the surface of the disk, the original binary signal is reproduced. At this time, the signal read from the surface of the disk is referred to as a radio frequency (RF) signal. The RF signal has a characteristic of an analog signal due to the physical and optical characteristic of the disk. Accordingly, the analog signal should be converted into a digital signal and this conversion necessarily needs binarization and a phase locked loop (PLL) process. A variety of binarization means are available, and among them a viterbi decoder is known as a decoding apparatus capable of obtaining a binary signal having the least errors. Also, the viterbi decoder is known to be capable of obtaining a binary signal in an optimal condition to suit the characteristic of a channel and to have a better performance than that of a simple sign detection circuit or a run length correction method.
FIG. 1 is a block diagram of a conventional art data reproduction apparatus having a vterbi decoder. An analog signal 101 read from an optical disk (not shown) is converted into a quantized digital signal 102, by being sampled and held by an analog-to-digital converter 110. An offset cancellation unit 120 compensates the DC component of the quantized digital signal 102 using an offset signal 103. An equalizer is usually implemented by a finite impulse response (FIR) filter 130 and amplifies each input signal 104, which is the digital signal 102 compensates by the offset signal 103, that is delayed and then input, in a predetermined frequency band so that the characteristic of a channel becomes clear. Since a branch metric generator (not shown) inside a viterbi decoder 140 generates a state metric by obtaining the difference between each reference level and an actual input signal 105, a reference level 107 input to the viterbi decoder 140 has a great influence on the performance of the viterbi decoder 140. However, due to the physical characteristic of a disk and situational changes, a reference level 107 having an optimal condition for a signal input 105 from each medium is different, and a reference level 107 maximizing the performance of the viterbi decoder 140, should be determined.
One method to solve the above problem is to add a level detector 150 to the apparatus, as shown in FIG. 1. This method or device is disclosed in detail in Korean Patent No. 2000-00965. The level detector 150 generates an optimum reference level 107 which is input to the viterbi decoder 140 from the output 105 of the FIR filter 130. The level detector 150 determines one of reference levels 107 used in the viterbi decoder 140, including +/− maximum level, +/− medium level, and zero level, by monitoring the output 105 of the equalizer 130. Then, by using the determined value as a determined level of the viterbi decoder 140, the error ratio of data bits is reduced and the data detection 106 performance is improved. Each of the components 110, 120, 130, 140, 150 receives a signal 109 from a phase locked loop unit 160, which phase loop locks the input signal 104.
However, in the conventional data reproduction device in FIG. 1, an optimum reference level is selected by selecting a signal 107 having a predetermined level, such as +/− maximum level and +/− medium level. Accordingly, if noise occurs in a determined level, this level 107 does not correspond to the original reference level, but to another level, causing serious problems in the decoding procedure. Generally, the higher the recording density of an optical disk, the lower the quality of a signal 106 reproduced. Generally, tangential tilt or radial tilt caused by deformation of a disk substrate or a pickup apparatus creates noise in this high recording density disk, and the increasing error ratio due to this noise causes more serious problems in an ordinary disk reproduction device.